To achieve a high-efficiency SHG device, the phase needs to be matched between the fundamental wave and the second higher harmonic wave (hereinafter simply referred to as the SH wave), and a variety of studies relating to this have been made. Among others, the QPM-SHG device using the quasi-phase-matching (hereinafter simply referred to as the QPM) is most superior. The QPM is a method of compensating the difference in the propagation coefficient between the fundamental wave and the SH wave through the periodic polarization inversion so as to match the phase.
Further, it has been generally known that, if a light of the first wavelength is mixed with and excited by an excitation light of the second wavelength by using a nonlinear optical crystal having the nonlinear optical effect (the sum frequency optical mixing effect), a light of the third wavelength can be obtained, and that a constant relationship is obtained among them. That is, in the sum frequency optical mixing (photon mixing) having the nonlinear optical effect, if the first light (wavelength λ1) and the second light (wavelength λ2) are mixed and propagated, the third light (wavelength λ3) is obtained, and the relationship 1/λ1+1/λ2=1/λ3 is established among them.
Those relating to Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2 relate to the device having the sum frequency optical mixing effect.
The optical device which converts an image formed by an electromagnetic wave of a constant wavelength into an image formed by an electromagnetic wave of another wavelength, particularly when the above first wavelength forms the infrared light, i.e., when the infrared imaging measurement is performed, is an extremely important technique as the “eye” in the field of the global environment and the space environment remote sensing. Currently, infrared cameras using the pyro device array, for example, are used. These publicly known infrared cameras are extremely expensive and thus difficult to be easily applied to other fields than specialized industries such as the space and defense industries, and also have difficulty in responding at a high speed equal to or faster than a nanosecond.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-31827
Non-Patent Document 1: “Design of Highly Efficient SHG Bule Light Source by Using a Propagation-Mode Control Method,” Makoto Minakata and Shigehiro Nagano, Shizuoka University Electronics Research Institute Study Report, 1999, Vol. 34
Non-Patent Document 2: “Study on Small Size Polarization Domain Inversion for High-Efficiency SHG Device,” Shigehiro Nagano, Makoto Minakata, et al., Shizuoka University Electronics Research Institute Study Report, 2001, Vol. 36